Can openers used for opening cans of preserved produce are well known. In general, they cut the lid of the can by utilizing a combination of a traction wheel and a cutting wheel. The traction wheel is usually driven and acts as a reaction surface against the can wall or can seam. It acts to drive the can opener around the top lip (seam) of the can while the sharpened cutting wheel rotates and cuts through the can.
The most common type of can opener available is the one that cuts the top lid of the can at a location inside the top circumferential seam of the can. The disk-like cut lid is then removed to gain access to the can contents through the top of the can. A serious problem with this mode of opening a can is that the cutting blade cuts down through the circumference of the circular lid and tends to contact the sterilized preserved contents of the can. This is a problem if the cutting blade is contaminated from previous use and bacteria and debris have accumulated on the cutting blade. Another problem with this type of can opener is if the cutting blade is not particularly sharp, it will not cut the lid cleanly. Small metal shavings and cuttings are created and they fall into and contaminate the contents of the can. A further problem is that if the entire circumference of the circular top can lid is cut, the lid with its contaminated exterior side often falls into the can and contaminates the contents. Also, the lid can often be difficult and messy to remove from the interior of the can.
To address these problems, can openers have been developed that are designed to cut the outside seam of the can, rather than the lid. Examples of these can openers include U.S. Pat. No. 3,719,991 to French; U.S. Reissued Pat. No. 27,504 to Smith; U.S. Pat. No. 1,935,680 to Von Wolforsdorf; U.S. Pat. No. 4,782,594 to Porucznik et al. and U.S. Pat. No. 3,510,941 to Fyfe. All these patents disclose a can including a pin sliding in an arcuate slot for engaging and locking the can opener on the can to be opened. While these arrangements work adequately, over time there is a tendency for the moving parts to wear.
The result is that the engaging and locking function of the opener is impaired thereby leading to difficulty in cutting the can and keeping the opener in position on the can.
U.S. Pat. No. 5,121,546, granted Jun. 16, 1992, to the subject inventor, Wun C. Chong, discloses an effective solution of the above discussed wear problem. In the can opener disclosed in U.S. Pat. No. 5,121,546, there are thrust surfaces and a separating mechanism that can be introduced between the thrust surfaces. The separating mechanism, typically a ball bearing, is introduced between the thrust surfaces and moves a movable thrust surface away from a fixed thrust surface to separate a movable wheel, usually the traction wheel, and a cutting wheel. Using this mechanism, the can opener is brought to the cutting position. The traction wheel can then be rotated to cut the seam of the can. While the can opener disclosed in my U.S. Pat. No. 5,121,546 has proved to be extremely effective, experiments with various groups of operators have shown that a certain manual dexterity is required in order to effectively operate the can opener.
U.S. Pat. No. 5,367,776, granted Nov. 29, 1994, to the subject inventor, Wun C. Chong, discloses a design of can opener comprising a housing having a manually operable handle. The cutting wheel has a cutting edge for severing the seam of the can wall, with the cutting wheel defining a cutting wheel axis. The can opener also has a traction wheel which has a gripping surface. This gripping surface engages the can with the traction wheel defining a traction wheel axis. The can opener also includes a mechanism for rotatably mounting the traction wheel and the cutting wheel in the housing such that their respective axes of rotation are substantially perpendicular and the wheels are positioned adjacent and spaced apart from each other to define a gap to accept the seam of the can to be opened. One of the wheels is movable towards the other wheel in order to engage and lock the can between the cutting wheel and the traction wheel so that the cutting wheel acts to sever the seam of the can wall. The traction wheel acts to move the can past the cutting wheel.
A first thrust surface is associated with the housing and a spaced, adjacent, second thrust surface is associated with the moveable wheel. The first and second thrust surfaces comprise cooperable cam surfaces which are rotatable relative to each other to reciprocate the first and the second thrust surfaces relative to each other between a first position, where the gap between the two surfaces is relatively wide, and a second position where the gap between the two surfaces is narrow and the can is engaged and locked between the cutting wheel and the traction wheel. A handle is associated with one of the wheels to enable the wheel to be manually rotated.